1. Field of the Invention
The present invention relates generally to electronics systems and, more particularly, to an electrostatic precipitator for removing zinc whiskers from cooling air for electronics systems.
2. Related Art
Computers such as servers and the like are housed within an electronics enclosure or chassis that provides multiple functions such as protecting operating components from damage and shielding against undesirable electromagnetic emissions. With the advent of data centers and the recent trend toward collocation facilities, such electronics enclosures are often configured to be mounted in a standard-size cabinet commonly referred to as a rack enclosure or cabinet. Such a cabinet can house multiple rack-mount collocation computers.
Thermal management within data centers is becoming increasingly difficult due to the continued increase in processing power of servers and other rack-mount collocation computers. Waste heat generated within such computers must be dissipated to avoid damage. Excessive heat, for example, can cause premature failures in processors, power supplies, disk drives and expensive plug-in cards such as fax modems, T1 trunk cards, RAID (redundant array of inexpensive disks) controllers and video-streaming cards, as well as other components.
Conventional data center installations use elevated or raised floors constructed from removable tiles. Elevated floors provide unrestricted space for the flexible routing of cables and power lines under the floor. One particular function of elevated floor systems is that they form a sub-floor duct or plenum for distributing cooling air. Typically, cooling air is forced through the plenum and enters the ambient air in the data center through gratings formed in certain floor tiles.
Traditionally, waste heat generated in rack-mount collocation computers was removed through the vertical distribution of cooling air from the plenum floor system. Conventional cabinets typically included fans mounted at or near the top of the cabinet. The fans draw cooling air up into the cabinet through an opening in the cabinet base. The cooling air is then exhausted from the cabinet into the ambient air in the data center.
More recently, manufacturers have developed servers with faster processing chips and greater input power in a smaller rack-mount enclosure. Because such servers require cooling air to be drawn through rather than around the rack-mount enclosure, cooling fans are now commonly integrated into servers. To provide on-board cooling fans with adequate airflow, rack cabinets have been redesigned to allow air to readily flow through the cabinet doors.
Data center floor tiles commonly include a steel, wood or wood-composite core with a steel bottom plate either hot-dipped or electroplated with zinc to prevent rust and corrosion. The electroplated zinc-coated tiles exhibit a peculiar behavior of having zinc filaments grow from various locations on the bottom surface. These zinc filaments are commonly referred to as zinc whiskers. Under stress or changing environmental conditions, the zinc atom structure separates from the steel and forms microscopic columns in a process known as atom migration. These columns of zinc, which grow from the bottom and sides of the elevated floor tiles, are approximately 2 microns in diameter, and grow at a rate of approximately 250 microns per year.
Zinc whisker contamination most commonly occurs when floor tiles of older elevated floor systems are disturbed. For example, when tiles are removed to gain access to the area under the floor to run cables or power lines, tiles are often placed one or top of another or are slid around on the floor. Such actions strip off thousands of zinc whiskers from the underside of the tile and introduce them into the air circulating in the data center. Zinc whisker contamination also often occurs simply with the passage of time. Zinc whiskers continually grow from the bottom of the floor tile into the stream of cooling air traveling through the raised floor plenum. Eventually, the zinc whiskers are severed from the floor tile by the passing cooling air. On-board cooling fans in rack-mount computers draw the zinc whiskers into the internal logic cages and power supplies. Once inside, the velocity of the zinc whiskers progressively diminishes due to the maze of components and electrical wires, facilitating the release of the zinc whiskers into the cooling air. The zinc whiskers, which are conductive contaminants, then settle on electronic components of logic cards and power supplies causing voltage or signal perturbations. Zinc whiskers can also cause catastrophic failures by shorting a power supply. Oftentimes malfunctions and data errors caused by zinc whiskers are transient and not repeatable because the zinc whiskers fuse and vaporize, or are repositioned when the rack-mount computer is removed for fault analysis.
The most common recommendation in the electronics industry to address the problems associated with zinc whiskers is to replace all accessible floor tiles and encapsulate those that are inaccessible. This is an extremely labor-intensive procedure involving specialized decontamination and encapsulation of air plenum surfaces. Another drawback of this and other disruptive procedures is that they increase the amount of zinc whisker released into the cooling air and ultimately distributed throughout the data center. A further drawback is that such a procedure often requires the computer systems supported by the elevated floor system to be taken off-line.
Other conventional approaches to addressing problems stemming from zinc whiskers have met with little success. For example, common filters are ineffective because zinc whiskers are small relative to dust and other common particulates. On the other hand, attempts to use filters capable of capturing zinc whiskers dramatically reduces airflow and cooling capacity in the data center. Other conventional approaches include coating printed circuit boards with a conformal coating, which is expensive, and separating high-voltage nodes of the printed circuit boards, which addresses only a subset of the problems caused by zinc whiskers, and which requires a redesign effort that could result in a printed circuit board which is too large for the server chassis.